The Surrogate Endpoint Biomarker (SEB) Core will serve as a resource and service for carrying out laboratory analyses related to this project. The core has developed, validated, and standardized sample collection, sample preparation, and sample analysis procedures for blood and skin biopsies described in this core. Additionally, we will continue to optimize methods for measuring SEBs to be used in the projects. The SEBs to be analyzed by the SEB Core will include histopathology, morphometry, agent levels (blood and skin biopsy), cell proliferation measured by immunohistochemical detection of proliferating cell nuclear antigen (PCNA), expression of p53 protein by immunohistochemistry, measurement of apoptotic rate (morphology and in situ TUNEL), and the development of assays for AP1 activity and UV dimer formation (immunohistochemistry). The SEB Core will oversee and coordinate the collection and processing of all samples related to this Program Project at the clinic site, including distribution to the Molecular Genetics Core. The SEB core will be responsible for training of personnel involved in the collection and processing of study samples. The core will perform SEB assays and will work closely with the Biometry Core to provide raw data for analysis and interpretation. Quality assurance and quality control procedures will continue to be developed by the SEB Core and will be supervised by the Biometry Core for sample acquisition, processing, and analysis procedures included in each of the projects.